Thermal aging technique development

At room temperature or body temperature, the oxidation of UHMWPE takes years to reach an appreciable level that may result in decay of mechanical performance. Thermal aging techniques were developed to accelerate the rate of oxidation of irradiated UHMWPE. The material behavior after accelerated aging is assumed comparable to naturally aged ones. The standard method [ASTM F2003 - 02(2008)] permits the evaluation of oxidative stability in a relatively short period of time, i.e. weeks. 

Finally, a few articles have appeared on chemiluminescence of polymers. This technique has been used to detect hydroxy radicals in wood oxidation,y-irradiation effects on polyethylene, oxidation of nitrile-butadiene rubber, rubber under stress,antioxidant efficiencies in polyethylene, reactions of peroxy radicals, stereoregularity in poly(propylene), colour development in epoxy resins and structural changes in thermally aged poly(phenylene sulfide). ... 

Photo-DSC on the other hand, is a much more recent technique which has been developed thanks to technological developments in thermal analysis and coupled techniques. Until very recently, it has been used mainly to study photopolymerization or photocuring reactions by measuring the heat of reaction. We proposed the use of this powerful technique to study polymer photo-aging, using the photo-DSC as an accelerated aging device and coupled in situ analysis of the modification of the morphology of the materials. In this case, the crystallizability of the polymer is used as an indicator of the structural modifications. 

Although the study of materials chemistry is a relatively new entry in both undergraduate and graduate curricula, it has always been an important part of chemistry. An interesting timeline of materials developments from Prehistoric times to the present may be found in Appendix A. By most accounts. Neolithic man (10,000-300 B.C.) was the first to realize that certain materials such as limestone, wood, shells, and clay were most easily shaped into materials used as utensils, tools, and weaponry. Applications for metallic materials date back to the Chalcolithic Age (4,000-1,500 B.C.), where copper was used for a variety of ornamental, functional, and protective applications. This civilization was the first to realize fundamental properties of metals, such as malleability and thermal conductivity. More importantly, Chalcolithic man was the first to practice top-down materials synthesis (see later), as they developed techniques to extract copper from oxide ores such as malachite, for subsequent use in various applications. 

While TMA is one of the older and simpler forms of thermal analysis, its importance is in no way diminished by its age. Advances in DSC technology and the appearance of dynamic mechanical analysis (DMA) as a common analytical tool have decreased the use of it for measuring glass transitions, but nothing else allows the measurement of CTE as readily as TMA. In addition, the ability to run standardized material test methods at elevated temperatures easily makes TMA a reasonable alternative to larger mechanical testers. As the electronic, biomedical, and aerospace industries continue to push the operating limits of polymers and their composites, this information will become even more important. During the last 5 years a major renewed interest in dilatometry and volumetric expansion has been seen. Other thermomechanical techniques will also likely be developed or modernized as new problems arise. 

In the characterization of building and construction materials, the most frequently analytical tool performed have been X-ray diffraction but also, thermal analysis and microscopic techniques. Nowadays, infrared and other spectroscopic techniques have become as a useful, non-destructive and easy technique to study the phase composition of initial but also the evolved materials due to their exposure to the climatic conditions. Moreover, by using this tool is possible the detection of crystalline but also the amorphous phases very frequently developed on certain cementitious materials, mainly at early ages. The infrared spectroscopy is used both to gather information about the structure of compoimds and as analytical tool to assess in qualitative and quantitative analysis of mixtures. 

The effects of these parameters and cross-linking in polymer cable insulations, aged in radiation and thermal enviromnents, were investigated. The results were then used to recommend standards for an OIT methodology suited for practical use, including the nuclear power industiy. Techniques to estimate error in (O.l.T.) thermograms interpretation and reproducibility were also developed (Mason and Reynolds 1997). 

Novel mechanical tests are being developed and shown to be useful tools to investigate thermal and structural relaxation. These include the modulated-temperature-thermomechanometry technique (mT-TM) which has been recently employed to investigate blends of core cross-linked (CCS) PS and PMMA (Spoljaric et al. 2011) and nanomechanical thermal analysis. By using silicon microcantilever deflection measurements, the latter technique can provide a measure of temperature-dependent thermal stresses and therefore investigate the influence of physical aging (Yun et al. 2011). 

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